首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   296252篇
  免费   4948篇
  国内免费   858篇
电工技术   5366篇
综合类   357篇
化学工业   43866篇
金属工艺   10884篇
机械仪表   9125篇
建筑科学   7262篇
矿业工程   1145篇
能源动力   7098篇
轻工业   27573篇
水利工程   2884篇
石油天然气   4061篇
武器工业   72篇
无线电   36809篇
一般工业技术   56410篇
冶金工业   55418篇
原子能技术   5582篇
自动化技术   28146篇
  2021年   2831篇
  2020年   2196篇
  2019年   2640篇
  2018年   4853篇
  2017年   4873篇
  2016年   5152篇
  2015年   3301篇
  2014年   5308篇
  2013年   13762篇
  2012年   8696篇
  2011年   10852篇
  2010年   8514篇
  2009年   9210篇
  2008年   10295篇
  2007年   10034篇
  2006年   8860篇
  2005年   8023篇
  2004年   7699篇
  2003年   7452篇
  2002年   7028篇
  2001年   6867篇
  2000年   6578篇
  1999年   6771篇
  1998年   17031篇
  1997年   11939篇
  1996年   9223篇
  1995年   7054篇
  1994年   6274篇
  1993年   6123篇
  1992年   4731篇
  1991年   4404篇
  1990年   4244篇
  1989年   3966篇
  1988年   3797篇
  1987年   3324篇
  1986年   3226篇
  1985年   3800篇
  1984年   3544篇
  1983年   3151篇
  1982年   3004篇
  1981年   3102篇
  1980年   2896篇
  1979年   2752篇
  1978年   2606篇
  1977年   3127篇
  1976年   3939篇
  1975年   2396篇
  1974年   2370篇
  1973年   2391篇
  1972年   1889篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Different types of constructed wetlands in a pilot-plant system were fed with identical municipal waste water to compare the sanitisation process in two-stage systems. With combinations of a vertical and a horizontal flow filter an E. coli reduction of 5 log10 with an E. coli influent concentration of 10(7) MPN/100 ml was achieved. Using different filter materials in each stage the total performance of the two-stage system was independent from the sequence of these materials. However, using coarser filter material in the first stage makes the filter less prone to clogging and is thus the preferential option with regard to operational reliability.  相似文献   
72.
The Mexican petrochemical industry, Morelos S.A. de C.V., is one of the biggest and more important petroleum industries in Mexico and Latin America. It has an activated sludge system to treat its wastewater flow, which is approximately 7,000 m3/d. The wastewater contains volatile organic carbon substances classified as toxics. The old surface aeration system was changed for fine bubble diffusers; however, one major drawback of the new aeration system is that the temperature in the bioreactor has increased due to the compression of the air, which at the compressor exit reaches 85 degrees C. This effect results in the temperature in the bioreactor attaining 32 degrees C during the fall, whereas in the spring and summer, the bioreactor temperature reaches higher values than 40 degrees C. The high temperatures reduce the microorganism activity and cause a higher volatilisation rate of volatile compounds, among other effects, which affect the performance of the biological treatment. This work was performed to obtain a better modelling of the wastewater treatment from the petrochemical industry. The model describes the effect of the temperature on the performance of the biological treatment. The model was obtained from tests that were carried out in laboratory reactors with 14 L capacity, which were operated at different temperatures (from 30 to 45 degrees C), with the same wastewater and conditions as the actual system.  相似文献   
73.
74.
The identification of adequate wastewater treatment for small communities is a complex problem since it demands a combination of data from different sources, such as aspects of the community and landscape, the receiving environment and the available wastewater treatment technologies. The Catalan Water Agency (Agència Catalana de l'Aigua) considered using an EDSS (Environmental Decision Support System) as a tool to help water managers select the most adequate treatment for the urban wastewater of nearly 3,500 small communities in Catalonia (Spain). From that moment, EDSS was applied to all the river basins in Catalonia. In this paper the authors present the results obtained for the 76 small communities located in one of these river basins: the Fluvia River Basin. The characteristics of the community used in the reasoning process of the EDSS, the list of selected wastewater treatment alternatives, the technical environmental justification for the selected treatments and the reasons for discarding, favouring or disadvantaging them are presented. Finally, some results for the Fluvia River Basin are compared with those obtained in other Catalan river basins with different characteristics in order to evaluate which are the significant features in identifying adequate wastewater treatments.  相似文献   
75.
76.
Graduates of clinical training programs were surveyed to determine the degree to which they have found various graduate school experiences useful in their professional work. Samples of academic clinical psychologists and practicing clinical psychologists reported time allocation and preference for various professional activities, perceived usefulness of various theoretical orientations, and the influence on their current professional work of 19 different graduate training topics. Results suggest that where differences exist, academic clinical psychologists are generally more satisfied with Boulder-model-inspired scientific training than are clinical practitioners. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
77.
Book review     
  相似文献   
78.
Dynamic-viscosity measurements are reported for liquid mixtures in the system formed by n-butyraldehyde and isobutyraldehyde.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 48, No. 2, pp. 321–322, February, 1985.  相似文献   
79.
There are some foods that contain mutagenic or carcinogenic agents, some of which occur naturally and others that may be formed during preparation or cooking. Several foods such as legumes, also contain natural antimutagens and/or anticarcinogens. Lupine is one such legume that contains high amounts of protein (40%) and oils (14%). About 90 species of lupine have been reported throughout Mexico. However, the use of this crop as a source of food has been limited by the presence of antinutritional agents such as phenolic compounds (PC), carbohydrates (CH) and quinolizidinic alkaloids (Qas). It has also been suggested that consuming these compounds can affect human health and may even reduce the risk of disease. The objective of this work was to determine the effect of PC, CH and Qas, isolated and quantified from Lupinus campestris on the mutagenicity of 1-nitropyrene (1-NP) as a model mutagen and we used the Salmonella typhimurium tester strain YG1024 by the Kado microsuspension method. The results indicate that L. campestris seeds have 11 mg (+)catechin equivalent g(-1) seed coat; 120.3 mg g(-1) seeds and 2.13 mg g(-1) seeds of PC, CH and Qas, respectively. 1-NP mutagenicity was inhibited by 86% for PC, 76% for CH and 75% for Qas at concentrations of 200, 512 and 13.6 microg/tube, respectively.  相似文献   
80.
We analyze the non-Fermi liquid behavior in the proximity of the quantum phase transition induced by the strong polarization of the electrons due to local magnetic moments in Ni x Pd1-x alloys. We use the renormalization group approach introduced by Hertz–Mi11is–Moriya (HMM) to estimate the temperature dependence of the electrical resistivity for the case of three dimensional itinerant ferromagnets. We study two different cases, namely, the clean and disordered ferromagnets, and argue that at the present time more experimental data are needed to decide if the HMM theory can accurately describe the physical properties in Ni x Pd1-x alloys.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号